1. Field of the Invention
The present invention relates to a semiconductor package used in electronic equipment such as digital multifunction printers digital cameras, and more particularly relates to electromagnetic shielding and capabilities.
2. Description of the Related Art
Cellular telephones and other electronic equipment having wireless communication functions, which perform communication using electromagnetic waves in a frequency band of several hundred MHz to several GHz have come into widespread use in recent years. As such equipment has come into widespread use, there are more instances of using common electronic equipment in close proximity to these equipment. As a result, there is demand for such common electronic devices to have immunity against external electromagnetic waves, so as to operate normally even if subjected to external electromagnetic waves of frequencies in the several hundred MHz to several GHz range.
On the other hand, electronic equipment which acquires images, such as digital copiers and digital cameras, have come to use solid-state imaging elements with higher sensitivity in order to realize higher image quality. Solid-state imaging elements are semiconductor elements of which many parts, such as parts for photoelectric conversion and image signal transmission, are formed of analog circuits. High sensitivity is realized by amplifying very weak electric signals by high gain. Accordingly, the higher the sensitivity is, the weaker the signals handled are. Receiving even very weak external electromagnetic waves, in some cases, may cause interference to occur between the circuit and such very weak external electromagnetic waves, leading to false detection of signals. Thus, such electronic equipment having higher sensitivity requires higher immunity against external electromagnetic waves.
Proposed in Japanese Patent Laid-Open No. 2011-54643 is a method of improving immunity of electronic equipment against external electromagnetic waves. A frame-shaped conductive member is disposed on the inner side of a lead frame formed of a high magnetic permeability material in an analog circuit (or mixed analog circuit including digital circuits) semiconductor package. This arrangement works by attracting external magnetic fields to the high magnetic permeability material on the outer side, generating an opposite magnetic field to the external magnetic field by an eddy current flowing through the frame-shaped conductive member, and cancelling out the external magnetic field by this magnetic field. This configuration is particularly effective in the frequency range of several kHz to several MHz, where AC magnetic field has high effective permeability.
The frame-shaped conductive member has electromagnetic shielding capabilities at frequency bands lower than a particular frequency corresponding to the dimensional size thereof. However, there is a problem that, in the frequency range that is higher than the aforementioned particular frequency, the electromagnetic shielding capabilities gradually degrade as the frequency increases. The reason is that, in such a high frequency range, the electric field becomes a factor which affects the immunity of the semiconductor package against external electromagnetic waves, in addition to the magnetic field. The particular frequency at which the electromagnetic shielding capabilities begin to drop is dependent on the size of the frame-shaped conductive member, and is around 750 MHz in the case of a conductive member 5 cm square. The frame-shaped conductive member needs to be formed smaller than the conductive member to handle higher frequency bands. However, there is a limit to how far semiconductor elements such as solid-state imaging elements can be miniaturized, and there is a possibility that the method described in Japanese Patent Laid-Open No. 2011-54643 cannot ensure sufficient electromagnetic shielding capabilities.
The present invention has been made in light of the above problems, and provides a semiconductor package where a semiconductor element is disposed within an opening portion within a frame-shaped conductive member, which is capable of suppressing degradation that can occur in the frequency range of several hundred MHz to several GHz, thereby improving immunity of the semiconductor circuit against external electromagnetic waves.